User-agent: Googlebot 
Disallow: /admin/

User-agent: Googlebot-Image 
Disallow: /admin/

User-agent: Googlebot-Mobile 
Disallow: /admin/

User-agent: msnbot 
Disallow: /admin/

User-agent: Mediapartners-Google 
Disallow: /admin/

User-agent: TasBot
Disallow: /admin/

User-agent: * 
Disallow: /